Update versions in post-dev15 branch to 2.1.0-beta1
Update versions in post-dev15 branch to 2.1.0-beta1

xasx/roslyn,jasonmalinowski/roslyn,wvdd007/roslyn,KevinRansom/roslyn,KevinRansom/roslyn,panopticoncentral/roslyn,jcouv/roslyn,Giftednewt/roslyn,AmadeusW/roslyn,davkean/roslyn,bkoelman/roslyn,tannergooding/roslyn,kelltrick/roslyn,gafter/roslyn,DustinCampbell/roslyn,stephentoub/roslyn,davkean/roslyn,tmeschter/roslyn,heejaechang/roslyn,KirillOsenkov/roslyn,jamesqo/roslyn,swaroop-sridhar/roslyn,bbarry/roslyn,jcouv/roslyn,xasx/roslyn,lorcanmooney/roslyn,heejaechang/roslyn,akrisiun/roslyn,sharwell/roslyn,weltkante/roslyn,Hosch250/roslyn,mattscheffer/roslyn,TyOverby/roslyn,CaptainHayashi/roslyn,khyperia/roslyn,AdamSpeight2008/roslyn-AdamSpeight2008,abock/roslyn,akrisiun/roslyn,paulvanbrenk/roslyn,VSadov/roslyn,AdamSpeight2008/roslyn-AdamSpeight2008,AnthonyDGreen/roslyn,AlekseyTs/roslyn,Giftednewt/roslyn,bartdesmet/roslyn,zooba/roslyn,bbarry/roslyn,CyrusNajmabadi/roslyn,nguerrera/roslyn,brettfo/roslyn,cston/roslyn,wvdd007/roslyn,paulvanbrenk/roslyn,dotnet/roslyn,zooba/roslyn,OmarTawfik/roslyn,ErikSchierboom/roslyn,KevinRansom/roslyn,tmat/roslyn,tvand7093/roslyn,MichalStrehovsky/roslyn,amcasey/roslyn,dpoeschl/roslyn,drognanar/roslyn,Hosch250/roslyn,cston/roslyn,mmitche/roslyn,AmadeusW/roslyn,VSadov/roslyn,aelij/roslyn,orthoxerox/roslyn,bkoelman/roslyn,mattscheffer/roslyn,reaction1989/roslyn,mavasani/roslyn,robinsedlaczek/roslyn,aelij/roslyn,ErikSchierboom/roslyn,shyamnamboodiripad/roslyn,jkotas/roslyn,MattWindsor91/roslyn,bartdesmet/roslyn,mmitche/roslyn,gafter/roslyn,jkotas/roslyn,physhi/roslyn,CaptainHayashi/roslyn,aelij/roslyn,Hosch250/roslyn,shyamnamboodiripad/roslyn,jmarolf/roslyn,gafter/roslyn,mgoertz-msft/roslyn,pdelvo/roslyn,pdelvo/roslyn,CyrusNajmabadi/roslyn,dpoeschl/roslyn,lorcanmooney/roslyn,mavasani/roslyn,sharwell/roslyn,kelltrick/roslyn,jeffanders/roslyn,yeaicc/roslyn,orthoxerox/roslyn,zooba/roslyn,KirillOsenkov/roslyn,weltkante/roslyn,tvand7093/roslyn,sharwell/roslyn,jasonmalinowski/roslyn,nguerrera/roslyn,jasonmalinowski/roslyn,abock/roslyn,mgoertz-msft/roslyn,mattwar/roslyn,genlu/roslyn,panopticoncentral/roslyn,amcasey/roslyn,dpoeschl/roslyn,heejaechang/roslyn,orthoxerox/roslyn,bbarry/roslyn,tannergooding/roslyn,tannergooding/roslyn,mavasani/roslyn,CyrusNajmabadi/roslyn,jmarolf/roslyn,tvand7093/roslyn,tmeschter/roslyn,weltkante/roslyn,KirillOsenkov/roslyn,AlekseyTs/roslyn,physhi/roslyn,drognanar/roslyn,jcouv/roslyn,eriawan/roslyn,physhi/roslyn,srivatsn/roslyn,swaroop-sridhar/roslyn,drognanar/roslyn,dotnet/roslyn,agocke/roslyn,jeffanders/roslyn,bkoelman/roslyn,pdelvo/roslyn,jeffanders/roslyn,genlu/roslyn,robinsedlaczek/roslyn,MichalStrehovsky/roslyn,Giftednewt/roslyn,davkean/roslyn,amcasey/roslyn,TyOverby/roslyn,mattwar/roslyn,MattWindsor91/roslyn,dotnet/roslyn,yeaicc/roslyn,MattWindsor91/roslyn,OmarTawfik/roslyn,AnthonyDGreen/roslyn,AnthonyDGreen/roslyn,diryboy/roslyn,bartdesmet/roslyn,kelltrick/roslyn,paulvanbrenk/roslyn,shyamnamboodiripad/roslyn,srivatsn/roslyn,brettfo/roslyn,khyperia/roslyn,tmeschter/roslyn,tmat/roslyn,AdamSpeight2008/roslyn-AdamSpeight2008,panopticoncentral/roslyn,eriawan/roslyn,swaroop-sridhar/roslyn,DustinCampbell/roslyn,reaction1989/roslyn,OmarTawfik/roslyn,lorcanmooney/roslyn,MichalStrehovsky/roslyn,jkotas/roslyn,AmadeusW/roslyn,brettfo/roslyn,MattWindsor91/roslyn,DustinCampbell/roslyn,mgoertz-msft/roslyn,jmarolf/roslyn,jamesqo/roslyn,ErikSchierboom/roslyn,agocke/roslyn,mattwar/roslyn,abock/roslyn,wvdd007/roslyn,khyperia/roslyn,yeaicc/roslyn,jamesqo/roslyn,diryboy/roslyn,tmat/roslyn,CaptainHayashi/roslyn,diryboy/roslyn,AlekseyTs/roslyn,nguerrera/roslyn,stephentoub/roslyn,stephentoub/roslyn,eriawan/roslyn,mattscheffer/roslyn,mmitche/roslyn,srivatsn/roslyn,robinsedlaczek/roslyn,akrisiun/roslyn,agocke/roslyn,TyOverby/roslyn,VSadov/roslyn,xasx/roslyn,reaction1989/roslyn,genlu/roslyn,cston/roslyn